I'm trying to clarify a point. According to an article I read, manufacturers of preloaded systems place a flag in the BIOS which is recognized during the setup of the OS when using an OEM disk. This eliminates the need for product activation of the OS. Therefore a machine built for delivery with Vista will accept a Vista OEM disk, but will require activation if an XP OEM disk is used and the reverse would be true if the machine was built for XP.
Lenovo recovery discs look for a Lenovo flag, if they see it it pre-activates. The flag is not XP or Vista specific as the system could (for instance) have Vista with an XP downgrade.
Vista was the first OS to use the OA marker - it was the SLIC 2.0 marker
When Windows 7 came out, this was updated, so Win 7 enabled systems will have a SLIC 2.1 marker.